The goals of this program are aimed at a better understanding of bone development and remodeling, and the endocrine factors that influence bone, such as parathyroid hormone and calcitonin. Toward this end we are studying the metabolism of two characteristic components of bone tissue, citric acid and hyaluronic acid, as well as the effects of certain vitamins and hormones on this metabolism. In addition, cell culture studies are now under way in an attempt to characterize the type of bone cell(s) that respond to these agents and the mechanisms which underlie the observed responses. These investigations will provide a clearer understanding of the biochemical events involved in such processes as bone resorption. We will continue as part of an overall program the studies on the biosynthesis of parathyroid hormone. BIBLIOGRAPHIC REFERENCES: Wong, G.L. and Cohn, D.V: Target cells in bone for parathormone and calcitonin are different: Enrichment for each cell type by sequential digestion of mouse calvaria and selective adhesion to polymeric surfaces. Proc. Nat. Acad. Sci. USA August 1975. Luben, R.A. and Cohn, D.V: Effects of PTH and calcitonin on bone: Simultaneous measurements of calcium, glycosaminoglycan and citrate metabolism. Fed. Proc. 34:337,1975.